The aim of this project is to investigate the roles of brain event- related potentials, attention, and information processing and their interrelationships in the etiology, pathology, and prognosis of psychiatric and neurological disorders. Major emphasis is on the diagnostic specificity of disorders of attention and cognition and the identification of the specific aspects or stages of information processing underlying observed decrements in performance. Concurrently recorded brain event-related potentials and performance on cognitive tasks are used to differentiate patterns of dysfunction in attentive mechanisms in subjects with diagnoses of seasonal affective disorder, schizophrenia, seizures, eating disorders, dyslexia, closed head injury, attention deficit with hyperactivity disorder, and Tourette's Disorder. A related objective of this project is to differentiate state versus trait attributes of these disorders to increase understanding of their etiologies. Brain event-related potentials are also used to investigate the role of altered neurochemical mechanisms by comparing drug-induced electrophysiological and behavioral effects with those seen in the various disorders. Psychological correlates are investigated by relating the data to extensive neuropsychological, psychiatric, and personality measures as well as to performance on behavioral tasks.